Solder Paste Research Articles

A New Low-Temperature Solder Assembly Technique to Replace Eutectic Sn-Bi Solder Assembly.

We successfully achieved low-temperature assembly by reflowing the 13.5Sn-37.5Bi-45In-4Pb quaternary eutectic solder paste and the SAC 305 solder ball together at 140 °C for 5 min. The wetting angle of the mixed solder joint is 17.55°. The overall atomic percent of Pb in the mixed solder joint is less than 1%, which can be further reduced or eliminated. Moreover, after aging at 80 °C for 25 days, we observed no obvious decrease in shear strength of the fully mixed solder joint, which is the most advantage of this assembly technique over Sn58Bi solder assembly. The Bi phase segregation at the interface is slowed down compared with Sn-Bi solder joint. This low-temperature assembly is promising to be applied in advanced packaging technology to replace the eutectic Sn-Bi solder.

Investigation on SMT Product Defect Recognition Based on Multi-Source and Multi-Dimensional Data Reconstruction.

The recognition of defects in the solder paste printing process significantly influences the surface-mounted technology (SMT) production quality. However, defect recognition via inspection by a machine has poor accuracy, resulting in a need for the manual rechecking of many defects and a high production cost. In this study, we investigated SMT product defect recognition based on multi-source and multi-dimensional data reconstruction for the SMT production quality control process in order to address this issue. Firstly, the correlation between features and defects was enhanced by feature interaction, selection, and conversion. Then, a defect recognition model for the solder paste printing process was constructed based on feature reconstruction. Finally, the proposed model was validated on a SMT production dataset and compared with other methods. The results show that the accuracy of the proposed defect recognition model is 96.97%. Compared with four other methods, the proposed defect recognition model has higher accuracy and provides a new approach to improving the defect recognition rate in the SMT production quality control process.

Analyzing the Overfitting of Boosted Decision Trees for the Modelling of Stencil Printing

Stencil printing is one of the key steps in reflow soldering technology, and by the spread of ultra-fine-pitch components, analysis of this process is essential. The process of stencil printing has been investigated by a machine learning technique utilizing the ensemble method of boosted decision trees. The phenomenon of overfitting, which can alter the prediction error of boosted decision trees has also been analyzed in detail. The training data set was acquired experimentally by performing stencil printing using different printing speeds (from 20 to 120 mm/s) and various types of solder pastes with different particle sizes (particle size range 25–45 µm, 20–38 µm, 15–25 µm) and different stencil aperture sizes, characterized by their area ratio (from 0.35 to 1.7). The overfitting phenomenon was addressed by training by using incomplete data sets, which means that a subset of data corresponding to a particular input parameter value was excluded from the training. Four cases were investigated with incomplete data sets, by excluding the corresponding data subsets for: area ratios of 0.75 and 1.3, and printing speeds of 70 mm/s and 85 mm/s. It was found that the prediction error at input parameter values that have been excluded from the training can be lowered by eliminating the overfitting; though, the decrease in the prediction error depends on the rate of change in the output parameter in the vicinity of the respective input parameter value.

Wettability and Rheological Behavior of Low Ag Lead-Free SAC/Graphene and Cobalt-Graphene Nanocomposite Solder Paste

Wettability and Rheological Behavior of Low Ag Lead-Free SAC/Graphene and Cobalt-Graphene Nanocomposite Solder Paste

Effect of alloy particle size and stencil aperture shape on solder printing quality

PurposeReflow solder joint quality is significantly affected by the ability of the solder to perfectly fill pad space and retain good solder joint shape. This study aims to investigate solder joint quality by quantitatively analyzing the stencil printing-deposited solder volume, solder height and solder coverage area.Design/methodology/approachThe dispensability of different solder paste types on printed circuit board (PCB) pads using different stencil aperture shapes was evaluated. Lead-free Type 4 (20–38 µm particle size) and Type 5 (15–25 µm particle size) solder pastes were used to create solder joints according to standard reflow soldering.FindingsThe results show that the stencil aperture shape greatly affects the solder joint quality as compared with the type of solder paste. These investigations allow the development of new strategies for solving solder paste stencil printing issues and evaluating the quality of solder joints.Originality/valueThe reflow soldering process requires the appropriate selection of the stencil aperture shape according to the PCB and the solder paste according to the particle-size distribution of the solder alloy powder. However, there are scarce studies on the effects of stencil aperture shape and the solder alloy particle size on the solder paste space-filling ability.

Impact of Ni-coated carbon fiber on the interfacial (Cu,Ni)6Sn5 growth of Sn-3.5Ag composite solder on Cu substrate during reflow and isothermal aging

In this work, a novel composite solder was fabricated by mechanically incorporating Ni-coated carbon fiber (Ni-CF) into the Sn-3.5Ag solder paste in an effort to improve the overall service capability, where the intermetallic compound (IMC) formation and growth is a fundamental issue for consideration. General findings indicated that the addition of Ni-CF did not significantly impact the processing properties of the base alloy, such as melting temperature and wettability, when the reinforcement fraction was less than 2 wt%. Isothermal aging tests were carried out to study the formation and growth of interfacial IMC layers between the composite solder and Cu substrate. The addition of Ni-CF into Sn-3.5Ag solder could effectively promote the formation of interfacial (Cu, Ni)6Sn5 phase during reflow but retard its growth in the solid-state aging. The addition of 1 wt% Ni-CF was believed to be more effective to restrict and reduce the subsequent growth rate of the IMCs during solid-state aging due to the initial formation of a thicker (Cu, Ni)6Sn5 layer after reflow.

Optimization of FC-CSP and MLCC Soldering Process Using Type 7 Solder Paste

To confirm the possibility of simultaneous bonding between Si chip and multilayer ceramic capacitors (MLCCs), vacuum reflow soldering is performed between a Si chip and each of 2012, 1608, 1005, 0603, and 0402 MLCCs using Type-7 Sn-3.0Ag-0.5Cu (SAC305) and Sn-0.7Cu solder pastes. To enable an unbiased comparison with the vacuum reflow process, the Si chip and MLCCs are bonded via thermo-compression (TC) bonding and hot air reflow soldering, respectively. The maximum void content of Si chip solder joints bonded via vacuum reflow is 8%. At the MLCC solder joints, the void content yielded by vacuum reflow is lower than that yielded by hot air reflow. The bonding strength of the MLCC solder joint afforded by vacuum reflow is higher than that afforded by hot air reflow. Vacuum reflow is superior to hot air reflow in terms of the void content and bonding strength of the MLCC solder joint. After performing a thermal cycle test (TCT), a crack appeared at the Si chip solder joint bonded by TC bonding. The Cu pillar/Sn-2.5Ag bump is susceptible to cracks after the TCT owing to the insufficient bonding layer thickness yielded; however, the SAC305 sample from vacuum reflow is stable. Meanwhile, (Cu,Ni)6Sn5, Ni3P, and Ag3Sn intermetallic compounds are formed at the MLCC solder joints and then further developed after the TCT. The results of this study indicate the possibility of co-bonding Si chip with MLCCs for semiconductor packaging.

Research on Printing Defects Inspection of Solder Paste Images

Solder paste printing is the first part of the surface mount process flow; its postprinting defect inspection is particularly important. In this paper, we focus on studying the printing defects inspection algorithm for solder paste on PCB (Printed Circuit Board) images. The work proposes a number of methods to enhance the defects inspection performance of solder paste printing: a regional multidirectional data fusion image interpolation method, which can achieve fast and high precision image interpolation; a method for detecting solder paste areas with better accuracy, efficiency, and robustness; an improved connected domain labeling method to reduce time complexity; and defects detection and types classification method, which extracts features and centroid of every solder paste region and completes the inspection by comparing with a standard image. The experiments show that the defects inspection algorithm can detect the most common types of defects with low time consumption, high inspection accuracy, and classification accuracy.

Selection of Solder Paste Inspection Machines by Multi-Criteria Decision Analysis

One of the most important factors to give an inspection automation decision is the precision of measurements taken by the inspection machine. This paper aims to provide help in the selection of an automatic optical inspection (AOI) machine for a printed circuit board (PCB) assembly line of an electronics manufacturer. Since the visual inspection of soldered surfaces on a PCB is a crucial step, AOI machines bring great speed and accuracy to the inspection process. The main goal is to find the best automatic inspection machine alternative among the three AOI machine offerings according to nine selection criteria by integrating coefficient of variation statistic with TOPSIS and VIKOR, which are well-known multicriteria decision analysis methods. For this purpose, three different brands of AOI machines have been tested for the same PCBs, with 10 different components. After calculation of TOPSIS and VIKOR rank scores, the coefficient of variation of rank scores for all components is obtained and the selection of the AOI machine is finalized.

Center detection algorithm for printed circuit board circular marks based on image space and parameter space

A highly efficient circle positioning algorithm, called the two-step optimization Hough transform (TSHT), based on multi-resolution segmentation is proposed to solve the problems of the offset Hough transform, namely, its large memory overhead, long time consumption, and low recognition accuracy. First, using the image feature of the printed circuit board (PCB) circular identifier, the target circle is obtained using adaptive image preprocessing, and then, images of an acceptable quality are separated by shape quality inspection to improve their robustness. Second, using effective interval sampling strategies and gradually controlling the accumulative interval of parameters, the TSHT algorithm reduces the memory overhead and quickly locates the center at the pixel level. Finally, the center at the sub-pixel level is found by the least-squares method for circle fitting. The experiments prove that TSHT, as a result of its high robustness, strong anti-noise capability, fast recognition speed, and accuracy, can be successfully applied to a vision positioning system of a solder paste printing machine.

A novel antioxidant and low-temperature Sn-Zn solder paste based on Zn@Sn core-shell structure

With the advancement of lead-free solder, Sn-Zn solder was once considered the best choice. However, the high activity of Zn limited its application. To solve the problems of serious oxidation of zinc in Sn-Zn solder, a novel Sn-Zn solder paste based on Zn@Sn core-shell structure was developed. The Zn particles with a diameter of 3.5 µm are coated with a Sn layer with a thickness of 1.5 µm, which improves the oxidation resistance of Zn particles. The effect of the weight ratio of Zn@Sn to the Sn particles on the type and thickness of the intermetallic compounds (IMCs) layer was investigated. The shear strengths of solder joints based on the Zn@Sn core-shell particles were increased by 44% compared with that of the commercial Sn-Zn preforms, after reflowing at 230 °C for 10 min. The fracture microstructure showed a mixed fracture mode with both ductile and brittle characteristics. The results demonstrate that composite solder paste based on Zn@Sn core-shell structure is a promising die attach material for power device packaging.

Predictive model of the solder paste stencil printing process by response surface methodology

PurposeThis paper aims to establish the predictive equations of height, area and volume of printed solder paste during solder paste stencil printing (SPSP) process in surface mount technology (SMT) to better understand the effect of process parameters on the printing quality.Design/methodology/approachAn experiment plan is proposed based on the response surface method (RSM). Experiments with 30 different combinations of process parameters are performed using a solder paste printer. After printing, the volume, area and height of the printed SAC105 solder paste are measured by a solder paste inspection machine. Using RSM, the predictive equations associated with the printing parameters and the printing quality of the solder paste are formed.FindingsThe optimal printing parameters are 175.08 N printing pressure, 250 mm/s printing speed, 0.1 mm snap-off height and 15.7 mm/s stencil snap-off speed if the target height of solder paste is 100 µm. As the target printing area of solder paste is 1.1 mm × 1.3 mm, the optimized values of the printing parameters are 140.29 N, 100.52 mm/s, 0.63 mm and 20.25 mm/s. When both the target printing height and area are optimized together, the optimal values for the four parameters are 86.67 N, 225.76 mm/s, 0.15 mm and 1.82 mm/s.Originality/valueA simple RSM-based experimental method is proposed to formulate the predictive polynomial equations for height, area and volume of printed solder paste in terms of important SPSP parameters. The predictive equation model can be applied to the actual SPSP process, allowing engineers to quickly predict the best printing parameters during parameter setting to improve production efficiency and quality.

Mechanical, photoelectric and thermal reliability of SAC307 solder joints with Ni-decorated MWCNTs for flip-chip LED package component during aging

PurposeThis study aims to study the mechanical, photoelectric, and thermal reliability of SAC307 solder joints with Ni-decorated MWCNTs for flip-chip light-emitting diode (LED) package component during aging. By adding nanoparticles (Ni-multi-walled carbon nanotubes [MWCNTs]) to the solder paste, the shear strength and fatigue resistance of the brazed joint can be improved. However, the aging properties of Ni-modified MWCNTs composite solder joints have not been deeply studied. In this research, the mechanical, photoelectric and thermal reliability of SAC307 packaged flip-chip LEDs with Ni-MWCNTs added during aging were studied.Design/methodology/approachCompared with SAC solder alloys, the effects of different contents (0, 0.05, 0.1 and 0.2 Wt.%) of Ni-MWCNTs on the photoelectric and thermal properties of composite solder joints were examined. To study the aging characteristics of composite solder joints, the solder joints were aged at 85°C/85% relative humidity.FindingsThe addition of an appropriate amount of reinforcing agent Ni-MWCNTs reduces the density of the composite solder to 96% of the theoretical value of the SAC solder alloy. In addition, the microhardness increases and the wetting angle decreases. Two different phase compositions were observed in the solder joints with Ni-MWCNTs reinforcement: Cu3Sn and (Cu, Ni)6Sn5. The solder joints of SAC307-0.1Ni-MWCNTs exhibit the highest luminous flux and luminous efficiency of flip-chip LED filaments, the lowest steady-state voltage and junction temperature. And with the extension of the aging time, its aging stability is the best. In short, when the addition amount of Ni-MWCNTs is 0.1 Wt.%, the solder joints exhibit the best wettability and the thinnest intermetallic compound layer. And the shear strength of the tested solder joints is the best, and the void ratio is the lowest. At this time, the enhancement effect of Ni-MWCNTs on the composite solder has been best demonstrated.Research limitations/implicationsThe content range of enhancer Ni-MWCNTs needs to be further reduced.Practical implicationsThe authors have improved the performance of Ni-modified MWCNTs composite solder joints.Originality/valueComposite solder with high performance has great practical application significance for improving the reliability and life of the whole device.

The influence of SACX0307-ZnO nanocomposite solder alloys on the optical and thermal properties of power LEDs

PurposeThis paper aims to present the results of investigations that show the influence of ZnO composite soldering paste on the optical and thermal parameters of power light-emitting diodes (LEDs).Design/methodology/approachZnO nanocomposite solder alloys were produced via the ball milling process from the solder paste Sn99Ag0.3Cu0.7 (SACX0307) and 1.0 wt% of ZnO nanoparticle reinforcements with different primary particle sizes (200 nm, 100 nm and 50 nm). Power LEDs were soldered onto a metal core printed circuit board. A self-designed LED test system was used to measure the thermal and optical characteristics of the LEDs.FindingsThe influence of the soldering paste on the thermal and optical parameters of LEDs was observed. In all solder alloys, ZnO ceramic reinforcement, at a level of 1 wt%, increased the thermal parameters of LEDs and decreased their luminous efficiency. Thermal resistance values were10% higher, and junction temperature change over ambient temperature was 20% higher for the samples soldered with composite solder pastes than the reference sample. At the same time, luminous efficiency dropped by 32%.Originality/valueThe results prove that ZnO ceramic reinforcement of solder paste influences the thermal properties of solder joints. As was proven, the quality of the solder joints influences the whole assembly.

Solder void size reduction in semiconductor package by vacuum reflow and pressure cure processes

PurposeSemiconductor packaging industry has in recent years tightened the tolerance criteria for acceptable solder void size in the semiconductor packages due to the high usage in automotive applications. Semiconductor packaging component makers have strengthened the quality of the solder joint and its electrical conductivity by controlling the maximum solder void size reduction from 10-15% to 5% or below over die size. This paper aims to reduce the solder void size to minimum level that current industry could not achieve and introduce a new soldering processes by combining vacuum reflow and pressure cure to effectively reduce solder void.Design/methodology/approachThis study is using the empirical data collection to prove the feasible in achieve the goal. It is an engineering approach. This research study is even considering sufficient data (>22 units) in each evaluation to represent the actual performance.FindingsSuccessfully eliminate all the hollow solder void that current industry claimed as solder void. EDX analysis showed that the compressed solder voids remained in the solder are filled with solid carbon-based substances which could be originated from the trapped flux residues. It is empirical data proven in feasibility stage.Research limitations/implicationsThe study is able to produce solder void-less. This method is suitable for high volume manufacturing process also. This may lead a new pave way for industry to resolve solder void problem. The current pressure cure machine could not apply more than 200°C temperature which limits medium and high temperature solder paste or alloy testing. Therefore, only low temperature solder alloy Pb37Sn63 was able to be evaluated.Originality/valueThis study is original and has not been published elsewhere to produce high efficiency product in semiconductor packaging performance in electrical path and heat dissipation. It also improves package reliability due to solder joint used as interconnect in semiconductor packaging.

Influence of the soldering paste type on optical and thermal parameters of LED modules

PurposeThis paper presents the results of the investigations of LED modules soldered with the use of different soldering pastes.Design/methodology/approachThe tested power LED modules are soldered using different solder pastes and soldering processes. Thermal parameters of the performed modules are tested using indirect electrical methods. The results of measurements obtained for different modules are compared and discussed.FindingsIt was shown that the soldering process visibly influences the results of measurements of optical and thermal parameters of LED modules. For example, values of thermal resistance of these modules and the efficiency of conversion of electrical energy into light differ between each other even by 15%.Practical implicationsThe obtained results of investigations can be usable for designers of the assembly process of power LED modules.Originality/valueThis paper shows the investigations results in the area of effective assembly of power LEDs to the metal core printed circuit board (MCPCB) using different soldering pastes (REL22, REL61, LMPA-Q6, OM-5100, OM-338-PT, M8, OM-340, CVP-390). It was shown that the best thermal and optical properties of these modules are obtained for the OM5100 paste by Alpha Assembly.

Understanding the Effect of Reflow Profile on the Metallurgical Properties of Tin–Bismuth Solders

Sn–Bi alloys are desirable candidates for soldering components on printed circuit boards (PCBs) because of their low melting point and reduced cost. While certain tin–bismuth solders are well characterized many new alloys in this family have been developed which need proper characterization. The following study looks at the behavior of four different Sn–Bi alloys—traditional 42Sn58Bi and 42Sn57Bi1Ag and two new tin–bismuth alloys—in solder paste during the reflow soldering process. Each alloy was processed using different reflow profiles that had varying times above liquidus (TALs) and peak temperatures. The PCBs were then analyzed to see how the processing variables influenced wetting, voiding, microstructure, intermetallic layer composition, and thickness. After analysis, the PCBs were then subjected to thermal cycling experiments to see how reflow profile impacted microstructure evolution. The results demonstrated that reflow profile affects properties such as metal wetting and voiding. It does not however, greatly impact key metallurgical properties such as intermetallic layer thickness.

Investigation of solder beading phenomenon under surface-mounted electrolytic capacitors

PurposeThe purpose of this paper is to study the solder beading phenomenon (referring to larger-sized solder balls) of surface-mounted electrolytic capacitors. Solder beading could induce failures by violating the minimal electrical clearance on the printed circuit board (PCB). In modern lead-free reflow soldering, especially in high-reliability industries, such as automotive, aeroplane and aerospace, detecting and preventing such defects is essential in reliable and cost-effective manufacturing.Design/methodology/approachThe large size of the involved components may block the view of automatic optical inspection; therefore, X-ray inspection is necessary. To detect the failure mode, X-ray imaging, cross-section grinding, optical microscopy and Fourier transformed infrared spectroscopy were used. High-resolution noncontact profilometry and optical microscopy were used to analyse component designs. The surface mounting process steps were also analysed to reveal their dependence on the issue. Test methods were designed and performed to reveal the behaviour of the solder paste (SP) during the reflow soldering process and to emphasise the component design relevance.FindingsIt was found that the reduction of SP volume only reduces the failure rate but does not solve the problem. Results show that excessive component placement pressure could induce solder beading. Statistical analysis revealed that differences between distinct components had the highest effect on the solder beading rate. Design aspects of solder beading-prone components were identified and discussed as the primary source of the problem.Practical implicationsThe findings can be applied in surface-mount technology production, where the total failure count and resulting failure costs could be reduced according to the findings.Originality/valueThis paper shows that component design aspects such as the low distance between the underside of the component and the PCB and blocked proper outgassing of volatile compounds of the SP can be root causes of solder beading under surface-mounted electrolytic capacitors.

Effect of stencil wall aperture on solder paste release via stencil printing

Solder paste printing is a process by which the correct amount of solder paste is applied to the printed circuit board via a stencil. The solder release from the stencil printing process very much depends on the type of solder paste and stencil conditions such as the shape of the aperture, size, and thickness of the stencil. This paper investigates the stencil condition in particular the stencil wall aperture and its relationship to the solder release ability. In this work, two types of stencil wall openings A and B were used, which differ in a different ways of cutting to achieve the wall aperture. The cutting process produced different surface roughness of the wall aperture of the stencil. Stencil printing was performed to print the solder paste onto the PCB pad. The release of solder paste was observed by solder paste inspection (SPI) and analyzed qualitatively and quantitatively. The results show that stencil B gives a better solder compared to stencil A. This is due to the smoother wall aperture compared to stencil A which has a roughened wall aperture. This shows that the performance of stencil printing in terms of solder printing quality is highly dependent on the surface roughness of the stencil aperture. Stencil quality is important as it affects the performance of solder paste printing, and this process is mainly carried out in the electronics industry. Therefore, understanding stencil conditions is important for electronic technology that uses solder printing.

Mixed Assembly of Lead-free Solder Joint: A Short Review

The transition from lead (Pb) to Pb-free solder has arisen the need for the development of the reliability of mixed assemblies solder joint research. Mixed assemblies are defined as solder joints that joint together with different compositions or solder forms for example Ball Grid Array (BGA) and solder paste. During the transition period of solder materials, mixed assemblies are still used in electronic packaging. In addition, Pb-free manufacturing has been forced to release some of the product categories since legislation banning the use of lead solder in electronic assemblies. This phenomenon causes health and environmental concern of the Pb solder used in electronic assembly. Hence, some electronic assemblies will continue to use traditional eutectic Sn–Pb solder paste while others will use Pb-free solder paste. This situation indicates that the use of mixed assemblies in electronics manufacturing is still inevitable. This paper presents a projection of the reliability of mixed assembly’s Pb-free solder joint.